This is a transcript of the Gastropod episode Hacking Taste, first released on March 14, 2017. It is provided as a courtesy and may contain errors.

NICOLA TWILLEY: All right…

CYNTHIA GRABER: Okay, cheers!

TWILLEY: One, two, three…

TINA ANTOLINI: It’s like lemonade.

KELLEY CARTER: It’s so weird! Why is this so delicious? What the hell? Wait, what have you done to me?!

GRABER: So, before one of our Pop-Up Magazine shows, a handful of the crew and performers let us put red pills on their tongues without having any idea what they were taking and what they were in for.

TWILLEY: Hey, we’re good people. And it’s not like we didn’t do it ourselves. But I must admit, it was amazing how easy it was to get people to take pills without telling them what they were.

GRABER: We’ll tell you what those pills were later on, but, for now, what you need to know is that we were screwing with their taste buds.

TWILLEY: That’s right, this episode, we’re going to get to the bottom of our sense of taste: how does it work and how can we mess with it?

GRABER: Why do we taste the things we taste? And can the answers to these questions help us hack taste to tackle some of today’s biggest health problems?

TWILLEY: You’re listening to Gastropod, the podcast that looks at food through the lens of science and history. I’m Nicola Twilley.

GRABER: And I’m Cynthia Graber. And before we reveal the secrets of one of the most important ways we interact with the world, we have some sponsors to tell you about.

(PRE-ROLL)

(MUSIC)

GRABER: So this is kind of a broad question, but what is taste?

ROBIN DANDO: Yep, that’s pretty broad.

TWILLEY: That’s Robin Dando. He’s an assistant professor of Food Science at Cornell University, and he specializes in the study of taste.

GRABER: Taste is one of our five senses. You know the ones: sight, sound, touch, smell, and taste. So taste, like smell, is a chemical sense. Our taste buds are detecting chemicals.

DANDO: The taste bud sits just below the surface of your tongue. We have a few of them around the insides of our mouths as well. But most of them are concentrated in the tongue.

TWILLEY: A taste bud looks kind of like a very tiny little yellow onion. It’s a spherical clump of cells, it has a little bunch of root-looking nerves coming out the bottom, like at the bottom of an onion. And at the top, it has a little hole or pore.

DANDO: Where they branch these little fingers out into the tongue looking for these stimuli.

TWILLEY: Those are like if you left the onion to sprout—those little green shoots, they’re like the taste bud fingers waving around on the surface of your tongue waiting for a chemical stimulus.

DANDO: So a stimulus that’s in solution, something that we either drink or something that we’re consuming and is dissolved in saliva, can activate receptors on the very tips of these cells and cause the cell to light up and send the signal on towards our brain saying that we detect something.

GRABER: The taste buds catch chemicals in a liquid. That’s part of what our saliva does, it takes everything in our food and transforms it into a liquid form.

TWILLEY: Each of the cells at the tip of those little fingers is configured to grab onto different chemicals—chemicals that trigger the basic tastes.

JOHN MCQUAID: You know, you drink a Coke and a sugar molecule comes sweeping by and boom, it attaches itself to a sweetness receptor. And that activates a signal inside the taste cell in the tongue that goes into a nerve and goes into the brain. And you’ll recognize that it’s sweet and it will feel sweet.

TWILLEY: That’s John McQuaid, the author of Tasty: The Art and Science of What We Eat. Just to be confusing, John’s book is really about flavor, more than just taste. In normal conversation, we tend to use taste and flavor interchangeably, but they’re not the same thing.

GRABER: As you might know if you’ve listened to our flavor episode, flavor is much more complex than taste. It’s the whole experience of eating a food, so it includes taste. But it’s much bigger and it’s influenced by many other aspects of a dish.

TWILLEY: As you’ll know if you try to eat with a heavy cold, flavor has a lot more to do with smell than it does with plain old taste. Flavor depends on the aroma chemicals that are sensed in our nose. Also, you should listen to that episode if you haven’t! It’s called Savor Flavor.

GRABER: And if you heard our episode called Crunch, Crackle, and Pop, you’ll also know that all sorts of other things can influence the flavor we experience. Sound is another one. Check out that episode, too.

TWILLEY: Heck, check out our entire back catalog while you’re at it! I say this without any bias: it’s all great. But so taste is just one part of our experience of food. And, on the surface, it seems super simple. I mean, really kind of basic. The general consensus is that there are only five main tastes.

MCQUAID: Bitterness, saltiness, sourness, sweetness, and umami—umami being savoriness.

GRABER: There are other tastes that scientists think we might be detecting, but those are still being argued over. So taste has two primary functions in humans. The first one: it helps us survive. Paul Breslin studies taste at Rutgers University and the Monell Chemical Senses Center.

PAUL BRESLIN: Taste is really a gateway for the entire gastrointestinal tract and is a basis for making the determination whether you should eat it or not eat it. Is it nutritious, is it toxic? Will this help sustain you if you eat it and that it has calories and nutrients and minerals and vitamins, or is it poisonous, and if you eat it you’ll die and that it will end you right there with one meal?

TWILLEY: So it’s important. The second function of taste is kind of like an early warning system for your metabolism.

DANDO: When we take food into our mouths, it’s one of our first encounters with that food. So, to get our body ready to be able to digest it, we can’t just have the food placed right in our stomach. It’s not ready for it. So we have to have the right kind of gastric juices flowing inside of our stomach. We have to have some motility to actually be able to move the food down. Maybe, if we’re eating something very sweet, we’re going to have to have our body prepared for that blood sugar hit with an insulin response.

TWILLEY: Robin told us that your taste receptors will trigger all of these responses depending on what they detect. So your stomach and your pancreas and so on—they’re all gearing up, getting ready for what’s about to hit them.

GRABER: That response happens even if the food never makes it to your stomach—scientists have studied this both in animals and in people. People swish sweet solutions around in their mouths and spit them out. And their bodies get primed for sugar. Your insulin goes up, for instance, even if you just put a piece of candy in your mouth and then spit it out.

TWILLEY: So those are the two functions of taste: the conscious yes or no signal in our mouths, and the unconscious metabolic response. But why these five major tastes? Why did we evolve to detect sweet, salty, sour, bitter, and umami?

MCQUAID: Humans are omnivores so it benefits us to be able to taste as much as we can. Humans have lived in every environment on Earth. This has helped tune our sense of taste this way and that. That whole evolutionary background helps give us the great variety of taste abilities that we have today and also accounts for the great variety of food that we eat and cuisine around the world.

GRABER: John says actually pretty much all of the things our ancestors might have put into their mouths—plants and bugs and other animals—they all contain chemicals that fall within one or more of those five major tastes. But out of all the potential foods we could eat, we have a particularly strong reaction to chemicals that trigger our sweet receptors.

TWILLEY: Sugars, in other words: fructose, glucose, sucrose. Those light up our sweet receptors, and, from there, our brains. And that makes sense. Sugar is one of the most concentrated source of calories there is, and we need calories to live.

MCQUAID: Scientists think that sugar is really a primordial pleasure experience, since sweetness, which is basically the experience of sugar, goes back to the dawn of complex life. So for five hundred million years, life has been responding positively to sugar. So it’s not surprising that humans do also. And really it’s largely out of our control, our reaction to it.

GRABER: Salt is another one—we did an entire episode on salt, which of course you should also go listen to. All mammals need salt to live—we can’t make it, so we need to find sources of it in the environment. Makes sense that we’d be able to taste it.

TWILLEY: And Paul told us salt also triggers a metabolic response, the way the taste of sugar triggers your body to produce insulin. In the case of salt, Paul has managed to show that your blood vessels will actually start relaxing a little if you swish salty water in your mouth, even if you spit it out. Your blood vessels know that to keep your blood pressure constant, you’ll need to pull in more water to counterbalance that incoming salt, and they prepare accordingly.

GRABER: The relationship between salt and blood pressure is actually quite complicated—our episode on salt goes into this in much more depth.

TWILLEY: But sugar and salt are tastes that we crave because they’re things that we need. Sour is a little different. Very sour things don’t taste good, which makes sense because strong acids damage our teeth and tissues. Some people say sourness evolved as a ripeness detector, and so we don’t like really sour things because our body is telling us to hold off and wait until the fruit or berry or whatever is ripe and ready. But Paul pointed out that our response to sour is more complicated than straight up dislike.

BRESLIN: Obviously we like mixtures of acid with with sugar.

GRABER: Like lemonade. But even without sugar, sour flavors can still be appealing.

BRESLIN: People actually do like low levels of sour taste. People will put a twist into a glass of water, a glass of seltzer water.

GRABER: Scientists aren’t quite sure why we like these low-level sour tastes. One theory is that sour points us to vitamin C. Most mammals can make vitamin C, but we humans can’t. So it’s crucial that we be able to detect the ascorbic acid in fruit that gives it that puckery taste. We need that vitamin C. But there are other places we find sourness appealing.

BRESLIN: And in the case of eating virtually anything that’s fermented, whatever that may be, whether it’s dairy being processed into cheese, or cucumbers being processed into pickles, what have you, there’s acid being generated by bacteria. Or, in the case of yeasts, if you’re making wine or beer. And we seem to like that low level of acidity—a little bit of sourness is pleasing to us.

TWILLEY: Our taste for that fermented sour, that could be beneficial in evolutionary terms, too. We all know that our gut microbes appreciate fermented foods. So perhaps our sour taste receptors were guiding us toward that, too.

GRABER: That’s sour, now onto another complicated taste—bitter. And yes, we’ve done an entire episode on bitter as well.

TWILLEY: We really have made a lot of episodes!

GRABER: Which is a good thing. It means we can just tell you all to go listen to them. But bitter’s a weird one. We have more bitter receptors that can taste more bitter compounds, maybe hundreds of compounds, if not more. That’s more than for any other taste.

TWILLEY: Things that taste bitter often contain chemicals that are toxic to us, at least in large doses. Most people in most cultures around the world will not and do not eat anything that’s very strongly bitter. It’s an evolutionary response to avoid poisons. But for foods that are only mildly bitter, it’s a different story. Sometimes we even seek them out.

GRABER: Paul told us that in the real world almost all the food that’s good for us also has low levels of toxins, otherwise known as bitter flavors. We learned to enjoy, maybe even crave, some bitterness so that we can get all the other great nutrients in those bitter plants. And Paul says there’s another evolutionary reason we might like bitter: almost all medicines taste bitter, too. So our ancestors might have developed a taste for self-medicating.

TWILLEY: The fifth and final major taste is umami. And it’s the most recent addition to the canon. A Japanese chemist proposed that umami should join sweet, salty, sour, and bitter back in 1908, but it wasn’t really recognized as a distinct taste with its own unique chemical triggers until 1985.

GRABER: You may have heard of the main chemical trigger for umami that the Japanese scientist had isolated from seaweed broth. It’s called MSG, or monosodium glutamate.

TWILLEY: If you translate umami from Japanese, it means a “pleasant savory taste,” and it’s a really mild taste compared to sugar and salt and bitter. Umami never gets very strong, and we don’t even like it by itself. So why can we taste it?

GRABER: The first thing you need to know is that glutamates primarily come about through a transformation of protein. As protein breaks down, it’s transformed into amino acids and ribonucleotides. And together this is what gives you glutamates.

BRESLIN: Savory taste is about tasting amino acids and ribonucleotides together as a cocktail. So it kind of begs the question then: when are we going to be exposed to pure free amino acids and free ribonucleotides, together at the same time? And really the only time you’re going to experience those is when a food is being broken down, it’s somehow decomposing. And there’s really only three ways that that happens.

TWILLEY: Fermentation, drying, and cooking.

GRABER: You’ll find lots of awesome umami flavors in cooked meats or parmesan cheese, or, yes, seaweed broth.

TWILLEY: And when you taste umami, you’re actually detecting pre-digested protein. Although that doesn’t sound that nice, it’s really good news for your body: you need those amino acids from protein to build cells.

GRABER: Mmm. Delicious pre-digested proteins. But really, all these stories we’ve just told you about why we taste what we taste and why we’ve come to enjoy these tastes—these are just theories. We don’t know exactly what our ancestors were tasting. It’s impossible.

TWILLEY: But you can find some clues for how evolution has shaped taste by looking at other animals and what they can taste. Like, for example, cats. Cats are carnivores, they don’t eat their veggies, and all they have left is an umami receptor.

GRABER: Penguins and dolphins and whales and lots of other sea mammals also have a poor sense of taste—John says they’ve lost a lot of taste receptors over evolutionary time.

MCQUAID: It may be because they’re just swallowing fish whole, so you don’t really have a need to taste them. Most of the taste experience occurs when you’re chewing something. So there’s a lot of that in the animal kingdom, where certain animals, you know, they don’t need to taste something and so it falls into disuse and kind of is evolutionarily filtered out.

TWILLEY: And there’s been plenty of time for that filtering to happen, because the sense of taste is incredibly ancient.

MCQUAID: It goes back to the origin of complex life on Earth. Because once you have complex life, which is more than just single cells floating around, which is multi-celled creatures, they have an inside and outside, and the outside has to detect what is food and what isn’t food. So it goes back at least five hundred million years.

GRABER: And this is why animals that live in the water still have taste receptors in what might seem like strange places. In a lot of fish, taste receptors aren’t just in their mouths.

TWILLEY: Tom Finger is a professor at the University of Colorado School of Medicine who studies taste, and a lot of his work has focused on fish.

TOM FINGER: So the taste molecules are dissolved in the water, and they can swim around and detect taste because the taste molecules are contacting the surface of their skin. So catfish, for instance, have taste buds scattered across their whiskers and the whole body surface.

TWILLEY: It turns outs out that we are more like catfish than you might think. Because we have taste receptors outside of our mouths, too. They show up on a lot of the tissues that interact with these external molecules in our environment. So, in us, the equivalent of catfish whiskers is the lining of your gut.

FINGER: So anything that’s still in your stomach is not really in you. You’re sort of like a giant donut. There’s a hole running all the way through you from mouth to anus and anything inside that is in some sense not really in you. So you have taste receptors throughout your G.I. tract going all the way from your mouth through your intestines.

GRABER: Paul says these likely have an anticipatory role, like the ones in our mouth do. The taste receptors in our digestive system, they also help prime the body for the nutrients that are about to be absorbed into our bloodstream. And that’s not all.

BRESLIN: There are also taste receptors in what I would call regulatory organs or metabolic organs. And that would include the pancreas, the liver, fat tissue, adipocytes themselves, the thyroid, and the brain. And what they’re doing we really don’t know. But it’s a safe bet that in a species like ours that they’re extremely important.

TWILLEY: Back in Colorado, Tom has been working on figuring out what some of these receptors on other parts of our body do. And he says by calling them taste receptors, we’re kind of missing the point.

FINGER: So the taste receptors, actually from the standpoint of biology, you can think of them as just tools and they’re tools for detecting chemicals. So the body can use these tools anywhere. And because we give them the name taste receptors we’re confusing function with the role in biology.

TWILLEY: One of Tom’s projects has been to figure out what the heck taste receptors are doing in our noses.

GRABER: Turns out, these receptors detect chemicals put out by a harmful bacteria in the air that we breathe and then tell our body to mount an immune response. Like in our mouths, the nose taste receptors are just chemical detectors.

TWILLEY: So that’s how taste works, and how it evolved. And now here’s the cool part: as we learn more about taste, we can start to hack it—for fun but maybe also for health.

GRABER: But before we tell you how to mess with your friends’ taste buds at your next dinner party: this week’s sponsors.

(MIDROLL)

TWILLEY: So one of the many intriguing things about taste is that, although it’s one of our oldest senses, it was kind of ignored by science for a long time.

MCQUAID: It’s much easier to study the detection of light for example or sound, because these are sort of shared experiences, whereas an experience of taste or or smell also which are both components of flavor is a subjective experience. And so basically once science tried to wrap its arms around this it failed. And so a lot of scientists kind of gave up.

GRABER: And it’s not just that it’s hard to study. We also ignored taste because scientists and philosophers have looked down on it—for thousands of years. John says the ancient Greeks considered it the lowest and grossest of the senses.

MCQUAID: There’s a historical tradition in Western culture that makes taste and smell, particularly taste, second-class senses because they’re tied to eating, which is a kind of a base activity, you know, devouring stuff, putting stuff in your mouth, chewing it. You know, it’s what animals do. And, of course, we’re animals. But it wasn’t considered a higher sense.

TWILLEY: Still, throughout history people had theories—about how many tastes there were, and how the tongue detected them. But until really quite recently most of what we knew about taste was… wrong.

GRABER: The most enduring myth of the past century—and it’s one that you might even have learned when you were a kid—it’s a myth known as the tongue map. And we can lay the blame for this mistake at the feet of Edwin G Boring.

MCQUAID: He was an influential twentieth-century psychologist.

TWILLEY: And he decided to write the definitive book on the history of the senses—a big tome. And while Mr. Boring was researching the taste section of his book…

MCQUAID: He came across this study that had been done—this was I think in the 40s, he was writing this—and he came across a study that had been done about 30 years earlier by a German scientist that looked at the sensitivity of the tongue to different tastes. And this study showed that depending on where you were on the tongue, the sensitivity to these tastes differed, sometimes by a little, sometimes a little bit more.

GRABER: You know, like, one part of the tongue was more sensitive to sweetness. Another part was slightly more sensitive to salt. The German scientist published his data in the early 1900s. And then decades later, Boring drew on that data to draw his graph.

MCQUAID: But it was an exaggeration: the original data, you know, there were very limited differences. And suddenly now there were huge differences in this graph.

TWILLEY: Because Boring was so influential, this tongue map idea spread through the scientific community.

MCQUAID: And then pretty soon that morphed into maps of the tongue that showed clearly demarcated areas, you know, like on a geographical map where there’s a border, a clear border. It’s like the tip of the tongue tastes sweet and the back is bitter.

GRABER: Soon, these maps swept popular culture as well.

MCQUAID: They appeared in textbooks and they were used in children’s scientific experiments in elementary schools and it kind of became the conventional wisdom that different parts of the tongue were anatomically devoted to different tastes.

GRABER: So Boring was totally wrong. But scientists didn’t figure out just how the tongue works, how the taste receptors work, until quite recently. And that’s because of a much better understanding of genetics.

TWILLEY: Back in 2000, John actually visited scientists at the NIH when they were first isolating taste genes.

MCQUAID: Essentially they were looking for a needle in a haystack.

GRABER: They knew what taste receptors were, and they knew that there were genes to express them, but they didn’t know how to match the two.

MCQUAID: And basically through kind of a sieve like process they managed to isolate a sweetness receptor and match it with its DNA code in the genome.

TWILLEY: The scientists were working with rats, but fortunately, the human gene and receptor for sweetness is pretty similar.

MCQUAID: So once they had that, finding the human version of it was quite easy. And once you have that you can begin to experiment. You can make copies of sweetness receptors yourself, put them in a petri dish, and see how they react to different substances: to sugar, to artificial sweeteners, et cetera, et cetera.

TWILLEY: And from there, you can begin to understand how the sensation of taste is triggered, how it’s sent to the brain, and, ultimately, how we perceive it.

GRABER: One thing scientists have figured out is that, as we said, Boring was wrong. Every taste bud on our tongue has multiple receptors and those pick up many different tastes. It is absolutely not true that one section of the tongue is dedicated to sweet. There may be very slight differences in sensitivity, but everything is being sensed everywhere.

TWILLEY: But we’re not all sensing it exactly the same. There are pretty significant individual differences. And where they come from—that’s something that Linda Bartoshuk has been trying to get a handle on for decades. She’s a professor at the University of Florida and kind of a legend in the taste world.

LINDA BARTOSHUK: Well, it all started when we were doing work in New Haven, Connecticut, and we were working on—the first genetic known taste was to something called PTC. It was a bitter compound and it was known since the 1930s that some people couldn’t taste it. So I was working on that problem, and we decided that the methods that had been used on the problem up to then were very old-fashioned and we were going to do something more modern. We were going to actually see how bitter this compound was, not just whether you could taste it or not, but how bitter it was. Well, it turns out the variation was simply enormous. And some of the people got such incredibly intense bitter taste from this, that we started calling them supertasters.

GRABER: Yes, Linda is the one who coined the term supertasters. A lot of listeners have asked us to do an episode on supertasters.

BARTOSHUK: Supertasters are people who experience particularly intense taste sensations, the most intense taste sensations that are experienced by any people. Those are supertasters.

TWILLEY: Once Linda and her colleagues identified this group and started studying them, they quickly realized that it’s not just bitter PTC that supertasters taste more intensely—its everything.

BARTOSHUK: Yes, it is. Sweet is more intense to supertasters by about a factor of two or three.

GRABER: There is actually a continuum—it’s not a yes or no, super taster or not. Linda herself is in the “not” category, she’s on the non-tasting end of the taste spectrum. But a lot of people fall somewhere in the middle.

TWILLEY: Most scientists estimate that roughly a quarter of us are what they call nontasters, about a quarter are supertasters, and the rest are sort of medium.

BARTOSHUK: Part of it has to do with how many taste buds you have. Taste buds are on the human tongue in structures called papillae. And fungiform papillae, the ones on the front of the tongue, if you—under magnification they look like little button mushrooms on your tongue. And supertasters have many many more of these than people like me do.

GRABER: We decided to test some of these things out when we were on tour with Pop-Up Magazine. First, we wanted to find out who could taste PTC. We got a whole group of people in a backroom in one of the theaters and told them to put a piece of paper on their tongue.

GRABER: Why are you nervous?

KELLEY CARTER: Because I don’t really know what I said yes to at this point, so I don’t know what’s about to go down.

TWILLEY: It’s definitely not drugs.

CARTER: I’m a role model so I hope it’s not like drugs or anything.

TWILLEY: I don’t know if it was peer pressure or what, but they all did it. They put these slips of paper on their tongues without even knowing what it was.

CARTER: Just put it on the tongue.

GRABER: Yep.

TWILLEY: Paper for me.

GRABER: Really? I totally taste it.

DOUG MCGRAY: Tastes really terrible. It’s bitter, it’s really bitter.

CARTER: Paper for me.

GRABER: Paper for you too.

CARTER: Yeah.

GEOFF MANAUGH: I have a very, very bitter taste in my mouth—it tastes like aspirin or something. Yeah, it’s bitter for me too.

GRABER: It tastes exactly like aspirin. I totally agree. Oh Tim, you look like you’re in pain.

TIM BUNTEL: Yeah, it’s dreadful.

TWILLEY: In our little group we had four bitter tasters: Cynthia, Tim, Geoff, and Pop-Up boss Doug McGrey. I had a little bit of a bitter aftertaste, but not enough to scrunch up my face like those guys.

GRABER: One of our fellow contributors, Kelley Carter—she didn’t taste anything. Neither did another couple of the Pop-Up crew, Tina Antolini and Anita Badejo. No bitterness. Just paper.

TWILLEY: You can try this at home—I ordered the PTC paper off Amazon. It was kind of amazing how different all our reactions were.

GRABER: So not everybody who tastes PTC—who tastes that bitter—is automatically a supertaster. But Linda says it’s the first step. You have to be able to taste it. But then supertasters taste it super intensely.

BARTOSHUK: Supertasting is much more than this initial bitter compound we first discovered, it happens to all taste. But is there some biological utility that made—were supertasters the originals, and there was a mutation that made the rest of us? I don’t know. Very interesting question. But my picture of this, I think about the Neanderthals wandering around. Or maybe the first humans of our type wandering around. And, by the way, women are more likely to be supertasters than are men, and that gives you a clue. So maybe when they moved into new territory the chief sent his wife out to check out the local plants and if she didn’t die, they were OK. And she didn’t die, they were safe. But you’d want to supertaster to do that because the supertaster would taste the bitter more intensely and bitter is a signal for poison.

TWILLEY: This ability to taste PTC—it’s really interesting. It evolved independently in humans and, in our closest relatives, chimps. That implies that having some of your population as bitter tasters has an evolutionary advantage for the species as a whole. Otherwise it wouldn’t persist in humans over time like this, and it wouldn’t pop up separately in other species.

GRABER: Tasting PTC or not seems to be largely governed by one gene. Being a supertaster is more complex—Linda suspects multiple different genes contribute, although she hasn’t identified them yet. But there are patterns in the population as to who is likely to be a supertaster or a non taster.

BARTOSHUK: For example, Caucasians have the fewest supertasters. And men have fewer supertasters than women, and this led one of my post-docs one to say white men can’t taste. But I told her she couldn’t say that because it’s politically incorrect.

GRABER: What’s funny is that all three of the white guys backstage at Pop-Up could taste bitter—and remember, that’s the first step towards being a supertaster. But the two African-American women couldn’t.

TWILLEY: While our group was awesome, it wasn’t exactly statistically significant. But so PTC strips are the first step. The next step in diagnosing whether you are a supertaster or not is to count your taste buds. This involves dying your tongue blue. Funnily enough, our Pop-Up buddies didn’t want to do that before the show. I don’t blame them—I made Geoff dump a teaspoonful of blue food coloring on his tongue and he looked really funny.

GRABER: I think maybe you gave him a little much.

TWILLEY: Yeah, I think maybe we maybe overdid it a little.

GRABER: At least you overdid it on Geoff.

TWILLEY: It was a test run. That’s what husbands are for.

GRABER: Of course, we didn’t read the instructions—there are instructions for this experiment online—we thought you just squeezed out some dye on your tongue and then looked to see what stuck and what didn’t, because blue dye doesn’t stick to taste buds. But it’s a little more complicated than that, so after Geoff spent many minutes swishing out blue water, we decided to tackle this more scientifically back at home. We found instructions at Scientific American—we’ll link to it on our website.

TWILLEY: So it turns out we’re both basically average. At least when it comes to this. And actually, this is not a bad thing.

BARTOSHUK: Now, supertasters are going to be a little bit fussier than other people, because they’re going to notice bitter whenever it’s present. And there are going to be foods they don’t like, like leafy green vegetables that tend to be bitter. So there’d be perhaps an advantage to non-tasting if you’re in an environment with a lot of bitter compounds that are safe. But what if you’re in an environment with a lot of bitter compounds that are dangerous? Now the supertaster has the advantage.

GRABER: Supertasters generally don’t eat as many vegetables, so they seem to be at a higher risk for colon cancer. But they also tend not to drink and smoke as much, so they apparently are at lower risk for head and neck cancer.

TWILLEY: Swings and roundabouts. But all you supertasters out there, you can stop patting yourselves on the back.

BARTOSHUK: In some sense it was a poor choice of name because super implies something special, great. I’m delighted that I am not a supertaster. It just means more intense. And the truth is, I look around at extreme supertasters and I don’t think they’re having as much fun with food as I am. Let me qualify that one step. We have looked at the pleasure that supertasters and others get from food. And if you look at the favorite food of a supertaster—they really love it. And you look at something they don’t like, they absolutely hate it. So the supertaster experience is a much larger hedonic range of extremes to like and dislike. I’m sort of more in the middle. I like a lot of things but not terribly much. The supertaster may like fewer. But the ones he or she likes, they get tremendous pleasure from. Now that’s interesting. For example, chefs tend to be supertasters. More of them than you’d expect by chance. Is this that has something to do with the pleasure they get from their favorite foods? We don’t know. I’d like to see somebody study that who knows cuisine more than I do.

TWILLEY: This phenomenon of supertasters getting more pleasure from their favorite food—given how central food is to our pleasure circuits overall, this has really interesting implications, beyond food

BARTOSHUK: I mean are supertasters kind of a different group? Are they hedonically more volatile? Do they get more pleasure from a lot of things? That’s a real possibility. We just don’t know yet.

GRABER: This question of pleasure is a really complicated one—whether or not you’re a supertaster is only one factor in whether or not you’re deeply enjoying your meal. For example, research Linda’s done shows that overweight people get more pleasure from their food than thin people.

TWILLEY: And that’s complicated too. Because that brings us to the connection between our sense of taste and obesity. We live in a world where sugar is everywhere but we’re built to love sweet so intensely.

MCQUAID: The signal from sugar is, you know, give me more sugar.

TWILLEY: And that was totally fine back when we encountered sugar very, very rarely—in fresh berries, maybe, if we were lucky in wild honey. Now, of course, we have sugar at our fingertips day and night. Robin Dando—he’s the food scientist at Cornell—he’s been studying the connection between taste and obesity for a few years now.

DANDO: It’s a cruel joke really that we’ve been put together to just go after things like sweet and fat and to really like them. We’re programmed to want this in high quantities, we’re programmed to kind of put on weight for the hard winter that might be coming. Because that evolutionarily that means that we might stick around for longer. So it’s kind of a cruel joke now that this isn’t really a problem anymore, but we’re still programmed the same.

GRABER: Robin’s been studying the sense of taste in mice. One thing Robin’s found is that as the mice become obese, they lose tastebuds. And he thinks there’s a connection.

DANDO: Now, a couple of caveats in there of course. One is that these are mice, these aren’t humans. But, as I say, it’s a strong indicator. And then two is: Does losing a handful of taste buds actually do enough to change a person’s eating habits? Again, we don’t know that for sure. We’re looking into both of those questions right now.

TWILLEY: So we don’t know for sure, but you can easily imagine that if somebody has fewer taste buds, they might be getting less sensation from their food.

DANDO: So if that level of reward is decreased, then there are a couple of obvious things you could do to combat that. One is you could just eat more. And the other is you can eat more intensely tasting stimuli, so more intensely tasting usually is going to mean higher calories. So if that’s the case then, that when somebody starts to put on weight they lose tastebuds, they are driven to consume more, then that means that they’re going to put on more weight, lose more taste buds, and be driven to consume more again. So it’s kind of a dangerous positive feedback loop that we think could have something to do with the obesity epidemic that we’re living in right now.

GRABER: Supporting his hypothesis that gaining weight reduces taste sensation, and that losing weight might bring it back, Robin says there’s some evidence that people who lose weight quickly after gastric bypass surgery are more sensitive to taste afterwards.

TWILLEY: He’s also found that there are hormone receptors in your taste buds, too. They’re picking up on circulating hormones like leptin, which signals us to feel full. Those hormone levels change in obese people too. So that could also be affecting their experience of taste.

GRABER: And so maybe in there future there’ll be a way to use these taste-related phenomena to help people lose weight.

DANDO: So there are a lot of issues that happen with the body when someone becomes obese. And this would only be one of them. But if there is a portion of the process of becoming obese that could be attributed to the taste buds, then we’d really be interested in trying to kind of put that right, to kind of hack the taste bud to make it do things that we want people to do in terms of food choice, then I think that’s a really exciting idea.

TWILLEY: This is all just speculation right now—we don’t know enough to start hacking our taste buds to try to reverse obesity. But we do know that our sense of taste can be manipulated and changed, for all sorts of reasons.

GRABER: Like take pregnant women. All of a sudden things that used to taste good are suddenly disgusting. They throw up more frequently. Basically, their hormonal changes are making them more sensitive to potential toxins, more sensitive to bitter flavors. Children are the same, they’re really sensitive to bitter when they’re young. These are two super vulnerable groups, so it makes sense from an evolutionary perspective that they’d reject bitter and potentially poisonous foods.

TWILLEY: What you eat—your culture, your memory associations—that has a really strong impact on your sense of taste, too. John told us about a group of indigenous Peruvians who are all PTC bitter tasters. But where they live, one of the staple foods that they rely on is this really, really bitter potato relative. And so they seem to have reset their bitter taste perception—lowered it to the point where they can all eat and enjoy this potato, even though their genes would seem to indicate otherwise.

GRABER: So even if you are genetically sensitive to PTC, it doesn’t mean you can’t learn to enjoy bitter flavors. I taste PTC pretty strongly and I love bitter. Other tastes can be reset, too—we humans are really malleable. Robin told us about research showing that if you start eating food with less salt or less sugar in it, you become more sensitive to salty and sweet foods.

TWILLEY: There’s even some evidence that your mood affects how things taste. Robin has been working on this, too.

DANDO: So our model was we set up a stand at the hockey game at Cornell. If you’re interested in sports and going to Cornell then you’re probably going to the men’s hockey game.

GRABER: He found that enthusiastic fans whose team won, their food tasted better. But if the team lost, there went that delicious hot chocolate. Not so delicious anymore.

TWILLEY: And this makes sense, because there are those hormone receptors in the taste bud. And one of the hormones they pick up on is serotonin. Serotonin levels are connected to happiness versus depression. So there’s lots of interesting new science happening here too.

DANDO: There is a group that looked at SSRIs, so these are selective serotonin re-uptake inhibitors. So probably around about the most prescribed type of antidepressant in the country. And found that indeed people do start to perceive tastes, particularly sweet taste, as being different when they have have a lot of these antidepressants inside their body.

GRABER: All of this—mood and antidepressant research, the taste bud sensitivity and obesity research—all of this might help scientists hack our taste buds in the future to improve our health. But there are some fun ways to hack our taste buds today. Nicky had the chance to try something that I’m super curious about.

TWILLEY: It was when I was over in London.

EMMA ZHANG: Hi. My name is Emma Zhang. And we are at the Mixed Reality Lab in City University London. So we have this device over here which is a small device which you can put in your mouth and you will feel a virtual taste sensation.

TWILLEY: Basically there are two silvery plates hooked up to a set of wires. And you put the tip of your tongue in between them. Which I did. And then Emma electrocuted my tongue.

TWILLEY: Right, here goes. Oooh! Ahhh!

ZHANG: Yeah.

TWILLEY: Oh my god. That was ridiculous. Can I do it again?

TWILLEY: The taste she sent me was super sour. This is how it works.

ZHANG: So, for example, when we put something on our tongue, the chemicals will translate into electrical signal in our brain, and what we are doing here is to reproduce those electrical signals. So you will feel the same taste as if you are biting a lemon.

TWILLEY: The idea that Emma and her colleagues have is that you could build this kind of digital taste into cutlery, so your ice cream, say, would taste sweeter on an electric spoon. I don’t really know that I would sign up for getting my tongue electrocuted on a regular basis though.

GRABER: Doesn’t sounds like so much fun to me either, but I’d love to try it once. Some day. There’s another way to trick your taste buds. We used a pill—it’s an extract from a tropical African fruit called a miracle berry. What you do is you take the pill and slowly let it dissolve and coat your tongue. We handed them out to everyone in the dressing room. Then we handed them slices of lemons and limes.

DOUG MCGRAY: My new favorite food is lemon and pills.

TWILLEY: I could eat this whole lemon. Why didn’t we get more lemons?

GRABER: Oh my God, this lime is amazing.

TWILLEY: Everyone was just sticking whole chunks of lemon and lime into their mouths like they were apple slices. Then we moved on to something that’s already pretty sweet: strawberries.

TINA ANTOLINI: This is my worst nightmare. Everything is sweet.

MCGRAY: Intensely sweet.

GRABER: Oh my God, it’s way too sweet for me.

MCGRAY: Too much candy.

GRABER: Like it’s been dipped in sugar.

TWILLEY: It’s kind of disgusting.

GRABER: It’s a strange day when strawberries are so sweet that we’re calling them disgusting. So Linda says scientists don’t know exactly how miracle berries work, but here’s the leading theory: there’s a protein in the fruit that has sugar molecules on it. The protein attaches to your tongue with the sugar just out of reach. Then if you eat something acidic, like a lemon, your taste buds pucker, and they access the sugar molecules, too. So the lemon now tastes like it’s been coated with sugar.

TWILLEY: We didn’t stop at fruit, though. We tried beer and olives and blue cheese too. The olives—which, I love olives—they were just pure salt. Completely inedible. And the blue cheese was too salty and not funky and a little bit sweet.

GRABER: So that means that the scientific theory maybe doesn’t quite explain it all, because if it’s a protein with a sugar molecule attached, why would bitter and salt get so much more intense? Mysteries left to solve.

TWILLEY: This is another one you can easily try at home: we have a link to buy miracle berry pills on our website. Just be aware that if you go out for lunch afterward, like I did, your sandwich will taste disgusting.

GRABER: Linda says the effect lasts from about 15 minutes to about an hour and a half, depending on how strong your saliva is.

TWILLEY: So hacking your taste buds is possible. It works. But can we use it to achieve our health goals?

GRABER: There’s some evidence that this doesn’t work as intended. One way many of us hack our taste buds on a regular basis already is by consuming artificial sweeteners: these are non-sugar chemicals that trigger our sweet taste receptor, but our bodies don’t get any calories from them. Scientists have been showing that replacing sugar with artificial sweeteners isn’t helping people lose weight. In fact, with artificial sweeteners, people might actually be eating more. Maybe because our body is primed for sugar but we’re not getting those calories—and that triggers a whole set of reactions.

BARTOSHUK: You know and we should pay more attention to that. And by the way, that could be true of everything we do. For example, when you make acid stay sweet with miracle fruit the body’s expecting sugar. If we were really eating a lot of it, would that have consequences? It probably would. We ought to keep an open mind about that. Because when we come up with these things, it’s not nice to trick Mother Nature. She sometimes has her ways of getting even. And it’s very, very important to try to think of how things could go wrong. That’s our job as scientists.

TWILLEY: So we need to be careful. But this uncertainty—this is what makes the science of taste really exciting. It’s still such an open field. Robin told us that scientists are still trying to figure out exactly how sour works, for example. And there are lots of scientists trying to show that we have more than five basic tastes.

GRABER: We’ll write about that in our sustaining supporters email—that’s for folks who give $5 an episode or $9 a month. You can sign up at Patreon or on our website. In any case, there is a lot more still to learn about taste.

TWILLEY: It’s funny—taste is one of the oldest tools we have to make sense of the world, and one of the least well understood.

(MUSIC)

(POST-ROLL)

TWILLEY: Thanks this episode to all the people we spoke with: John McQuaid, Linda Bartoshuk, Paul Breslin, Robin Dando, Tom Finger, Emma Zhang —we have links to their books and research on our website.

GRABER: And a huge thanks to our partners Tim and Geoff and our friends and colleagues who were on tour with us with Pop-Up Magazine. The backstage taste hacking was ridiculously fun, and you all were great sports.

TWILLEY: We’ll be back with a new season in four weeks. In the meantime, catch us on tour: our Boston Museum of Science show is sold out, but the Michigan State University Science Festival performance is first come, first served, no tickets necessary. See you there!